1. Field of the Invention
The present invention relates to a hemopurification apparatus, and more specifically to a hemopurification apparatus which permits removal of water from blood without loss of effective and useful constituents from the blood upon dialytic therapy of patients with chronic renal failure or heart diseases, enables more sophisticated hemopurification therapy through its combined use with a conventional hemodialyzer or the like, and materializes, by itself or through its combination with an adsorbent or the like, both size and weight reduction to such a significant extent that the apparatus is portable.
2. Description of the Prior Art
Conventional hemopurification methods include hemodialysis, hemofiltration, direct hemoperfusion, etc.
In hemodialysis, blood is caused to flow through one of two compartments divided from each other by means of a dialytic, i.e., semipermeable membrane such as regenerated cellulose or polyacrylonitrile while a dialysate is caused to flow through the other compartment. Waste metabolites in the blood, for example, urea, uric acid, creatinine, electrolytes and the like are removed owing to the difference in concentration between the blood and the dialysate and at the same time, a pressure is applied to the blood to remove water from the blood owing to the difference in pressure between the blood and the dialysate.
In hemofiltration, blood is caused to flow through one of two compartments divided from each other by means of an ultrafiltration membrane. By applying a pressure to the blood, waste metabolites in the blood, for example, urea, uric acid, creatinine, electrolytes, water and the like are removed, primarily, by filtration.
In direct hemoperfusion, an activated carbon adsorbent, high molecular adsorbent or the like is brought into contact with blood either as is or after coating such an adsorbent with a material having good biocompatibility with blood, so that Waste metabolites in the blood, for example, urea, uric acid, creatinine and the like are adsorbed and hence removed.
The above-described conventional hemopurification methods are however accompanied by the following drawbacks.
In order to remove water from blood by hemodialysis, filtration is effected by using a dialytic membrane in much the same way as an ultrafiltration membrane. The method however allows electrolytes and useful constituents to flow out along with water from the blood. When hemodialysis is performed, urea, uric acid and the like are also removed from the blood and the osmotic pressure of the blood is hence lowered significantly to such a level that it becomes lower than the osmotic pressure of body fluids contained in cells of the body. As a result, water is caused to penetrate from the blood into the cells and although water must also be removed from the cells for successful hemodialysis, the water contents in the cells increase conversely. In order to avoid such osmotic pressure reduction in blood, it is now practiced to increase the concentration of Na.sup.+ ions in a dialysate so as to increase the concentration of Na.sup.+ ions in blood. This approach is however not believed to be the best method for patients, because Na.sup.+ ions which are supposed to be removed from blood for successful dialysis are increased conversely. Further, hemodialysis requires a great deal of dialysate in order to maintain a suitable difference in concentration between the dialysate and blood. A dialysate as much as about 100 l is generally required for dialytic therapy of 5 hours. Corollary to this, it is difficult to reduce the dimensions and weight of the purification apparatus of a hemodialysis system.
In hemofiltration, useful constituents, electrolytes and the like are also caused to flow out, along with waste metabolites, for instance, urea, uric acid, creatinine, water, middle molecules (hereinafter abbreviated "M.M." for the sake of brevity) and the like, from the body into a filtrate separated from blood. Moreover, the filtrate has to be produced in a large volume in order to achieve sufficient removal of waste metabolites from blood. As a result, the water level in the blood is reduced excessively. It is hence necessary to replenish the thus-lost electrolytes, useful constituents and water after the hemofiltration but before putting the thus-filtered blood back into the body. This replenishment is called "replacement fluid". In general, about 20 l of replacement fluid is required for single hemofiltration therapy. Since this replacement fluid is put directly into the body, it must be very clean. Here again, it is difficult to reduce the dimensions and weight of the purification apparatus of a hemofiltration system.
Direct hemoperfusion is effective for the removal of waste metabolites in blood, for example, urea, uric acid, creatinine, M.M., etc. Its apparatus may be fabricated into a compact structure. Direct hemoperfusion is however unable to remove water from blood.